Interactive responses of Quercus suber L. seedlings to light and mild water stress: effects on morphology and gas exchange traits

? The combined effect of water stress and light on seedlings of forest species is a key factor to determine the best silvicultural and afforestation practices in the Mediterranean area.

? The aims of this work was (1) to determine the optimal light level for the early development of cork oak seedlings under mild water stress and (2) to test if the combined effect of water stress and light followed the trade-off, the facilitation or the orthogonal hypothesis.

? Shade reduced instantaneous photosynthetic rates and water use efficiency in cork oak. However, seedlings grown under moderate shade (15% of full sunlight) were capable to accumulate similar amount of biomass than those grown under more illuminated environments by increasing their specific leaf area. Absolute differences in net photosynthesis between light treatments were higher in well watered than in water stressed seedlings. However, the impact of both factors on overall growth was orthogonal.

? We concluded that cork oak development is impaired under deep shade (5% of full sunlight) but it can be optimal under moderate shade (15% of full sunlight) even under moderate water stress. Implications of these patterns on regeneration, cultivation and afforestation of cork oak are discussed.

     

Modified exponential nitrogen loading to promote morphological quality and nutrient storage of bareroot-cultured Quercus rubra and Quercus alba seedlings

Abstract

Exponential nutrient loading has been used to improve nursery fertilizer uptake efficiency of conifer seedlings, but the technique has received little attention in the culture of temperate deciduous hardwoods. This study examined responses of northern red oak (Quercus rubra L.) and white oak (Q. alba L.) seedlings to modified exponential nitrogen loading during bareroot nursery culture using a broad range of nutrient supply from 0 to 3.35 g nitrogen (N) per plant per season for 18 weeks in Indiana, USA. Seedling growth and nutritional parameters followed a curvilinear pattern that ranged from deficiency to toxicity with increased fertilization consistent with trends depicted in the proposed model for nutrient loading. Fertilization increased plant dry mass by 113–260% for red oak and 49–144% for white oak. Severe nutrient deficiency occurred under indigenous soil fertility, and limited phosphorus and potassium uptake were found to inhibit seedling growth at higher N supply. The sufficiency and optimum rates were determined to be 0.84 and 1.68 g N per seedling per season, respectively, under the current cultural conditions. Fertilization at 1.68 g N per plant increased N content by 40% in red oak and 35% in white oak. This approach may be used to help refine nursery fertilization practices in hardwood culture to produce high-quality seedlings for field planting.     

Physiological responses of seedlings of two oak species to flooding stress

The physiological responses of 2-year-old seedlings of Nuttall＇s oak （Quercus nuttallii） and Southern red oak （Q.falcata） with two treatments i.e., deep-drowning and shallow-drowning, were studied. Taxodium distichum was selected as a control. The survival rates of seedlings were calculated, the photosynthetic indices were detected by Licor-6400 photosynthetic system instrument, and the root activities of seedlings were tested by the method of triphenyltetrazolium chloride （TTC）. Results showed that： 1） By experiencing flooding for 76 d and recovering for 60 d after water was drained off, all seedlings survived under the shallow-drowning treatment. None of Q. falcata seedlings died in the deep-drowning treatment until the 49th day. The survival rate of Q. falcata in the deep-drowning treatment was 30%. 2） Within 61 d of waterlogging treatments, the net photosynthetic rate （Pn）, stomatal conductance （gs） and transpiration rate （Tr） showed a tendency of declining, but intercellular concentration of CO2 （Ci） increased. With the prolongation of flooding stress, the extents of variation for all indices under deep-drowning treatment were larger than those under the shallow-drowning treatment. The variation of Q. falcata in flooding stress was larger than that of Q. nuttallii. 3） The root vigor and alcohol dehydrogenase （ADH） activities were detected at the 61st day in flooding stress. Waterlogging obviously inhibited root activities. Shallow-drowning made root vigor of Q. nuttallii decreased by 11.7%, and for Q. falcata, by 51.88%. Shallow-drowning treatment had no remarkable effects on ADH activities of seedlings, but deep-drowning increased those of Q. nuttallii seedlings by 227.24%, and decreased those of Q. falcata seedlings by 59.22% in the meantime. We conclude that Q. nuttallii had a stronger waterlogging resistance than Q. falcata, but weaker than T. distichum.     

Growth and physiological responses of Quercus brantii seedlings inoculated with Biscogniauxia mediterranea and Obolarina persica under drought stress

Charcoal canker of oak is a common disease in the western regions of Iran, which has widely spread due to climate change and increasing drought in recent years. Biscogniauxia mediterranea and Obolarina persica are known as two agents of oak charcoal canker in Zagros forests causing the dieback of oak trees. The effects of charcoal disease agent pathogens on the growth and physiological response of two‐year‐old seedlings of Quercus brantii were evaluated under drought stress in greenhouse over a period of nine months. Survival was 21.7% lower in seedlings inoculated with B. mediterranea subjected to drought stress compared with control treatment. The length of lesions on stems was 68% more under charcoal pathogens in drought stressed compared with the length of lesions caused by charcoal pathogens only. On the other hand, stem lesion length caused by B. mediterranea was 25% greater than those caused by O. persica. Some morphophysiological characteristics were affected by charcoal pathogens alone and/or in combination with drought. Diameter, height and biomass decreased the most in seedlings inoculated with charcoal pathogens under drought stress. Pathogenic agents alone and in combination with drought stress reduced photosynthetic rates, stomatal conductance, transpiration, the maximum Rubisco activity (V_cmax), maximum photochemical efficiency of photosystem II (F_v/F_m) and xylem water potential. In general, drought increased the aggressiveness of fungus and intensification of their destructive effects in Quercus brantii. Moreover, there was no significant difference between the effect of B. mediterranea and O. persica on the morphophysiological parameters studied.     

Physiological, morphological and anatomical responses of Fraxinus mandshurica seedlings to flooding

Two-year-old Fraxinus mandshurica Rupr. var. japonica Maxim. seedlings were flooded to 8 cm above soil level for 70 days. The flooding treatment altered the growth, morphology, stem anatomy and ethylene production of the seedlings. Although flooding did not affect height growth, it stimulated diameter growth of the submerged stems by increasing both the number and size of wood fibers produced; however, the thickness of the cell walls of the wood fibers was reduced by flooding. In response to the flooding treatment, the seedlings formed abundant hyperhydric tissues, originating from the vicinity of lenticels on the surface of the flooded stems, and adventitious roots, which grew through the hyperhydric tissues. Aerenchyma tissues were observed in the bark of the adventitious roots. The flooding treatment did not affect dry weight increment of leaves and stems, but it reduced the total dry weight increment of the root system even though it promoted adventitious root formation. Flooding also enhanced ethylene production in the submerged portions of stems. The potential roles of flood-induced ethylene in cambial growth and adventitious root formation in flooded plants are discussed.     

Effects of soil flooding on leaf gas exchange and growth of two neotropical pioneer tree species

Schinus terebinthifolius Raddi (Anacardiaceae) and Rapanea ferruginea (Ruiz & Pavon) Mez (Myrsinaceae) are two neotropical pioneer trees with wide geographical distribution in South America, highly degree of adaptation to different soil conditions and intense regeneration in areas with anthropic activities. With the aim to recommend the use Schinus and Rapanea in gallery forest restoration programs, we conducted an experiment with the objective to analyze the capacity of these two pioneer trees to tolerate soil flooding, mainly by accessing the effects of flooding on leaf gas exchange, growth and dry matter partitioning. Seedling survival throughout the 56-day flooding period were 100 and 90% for Schinus and Rapanea, respectively. The mean values of stomatal conductance (g_s) and net photosynthesis (A) observed in the control seedlings were, respectively, 0.4 mol m^–2s^–1 and 14 mmolm^–2s^–1, for Schinus, and 0.5 mol m^–2s^–1 and 14 mmolm^–2s^–1, for Rapanea. On day 20 flooding reduced gs and A by 36 and 29% in Schinus, and 81 and 61% in Rapanea. At the end of the experiment, significant decreases were also observed for root and whole plant biomass, in both species. Based on the results, we concluded that seedlings of Schinus and Rapanea can survive and grow throughout a medium period of soil waterlogging, in spite of the alterations observed in their physiological behavior, such as the decreases in stomatal conductance and in whole plant biomass.     

Growth and gas exchange in field-grown and greenhouse-grown Quercus rubra following three years of exposure to enhanced UV-B radiation

Long-term effects of enhanced UV-B radiation were evaluated in field-grown and greenhouse-grown Quercus rubra L. (northern red oak), a species with a multiple flushing shoot growth habit. Seeds were germinated and grown in ambient, twice ambient (2x) or three times ambient (3x) biologically effective UV-B radiation from square-wave (greenhouse) or modulated (field) lamp systems for three growing seasons. Greenhouse plants in the 2x treatment had greater heights and diameters during the later part of the first year and into the second year, but by the third year there were no differences among treatments. There were no significant differences in growth among treatments for field plants. Enhanced UV-B radiation did not significantly reduce total biomass or distribution of biomass in either field or greenhouse plants. Net photosynthesis (3x), leaf conductance (2x and 3x) and water-use efficiency (3x) of greenhouse plants were greater in the enhanced UV-B radiation treatments in the second year but unaffected by the treatments in other years. None of the treatments affected these parameters in field plants. Dark respiration was increased by the 3x treatment in the first and third years in greenhouse plants, and by the 2x treatment during the second year in field plants. Enhanced UV-B had variable effects on apparent quantum yield and light compensation points. Chlorophylls were unaffected by enhanced UV-B radiation in both greenhouse and field conditions. Bulk methanol-extractable UV-absorbing compounds were increased only by the 3x treatment in greenhouse plants during the third year and by the 2x treatment in field plants during the second year. Overall, Q. rubra appears relatively resistant to potentially damaging enhanced UV-B radiation and is unlikely to be negatively impacted even in the predicted worst-case scenarios.     

Aboveground biomass and net primary production of semi-evergreen tropical forest of Manipur, north-eastern India

The aboveground biomass dynamics and net primary productivity were investigated to assess the productive potential of Dipterocarpus forest in Manipur, Northeast India. Two forest stands (stand I and II) were earmarked randomly in the study site for the evaluation of biomass in the different girth classes of tree species by harvest method. The total biomass was 22.50 t·ha-1 and 18.27 t·ha-1 in forest stand I and II respectively. Annual aboveground net primary production varied from 8.86 to 10.43 t·ha-1 respectively in two forest stands (stand I and II). In the present study, the values of production efficiency and the biomass accumulation ratio indicate that the forest is at succession stage with high productive potential.     

NaCl胁迫对青檀种子发芽率、叶气体交换和苗木生长的影响

在水培条件下,本文探讨了NaCl胁迫对青檀种子发芽率、叶气体交换和苗木生长的影响。研究结果表明,NaCl胁迫延长了青檀种子的发芽时间,特别是当NaCl浓度超过17mM(1.0g/L)时,发芽率明显降低;NaCl胁迫降低了青檀叶的呼吸速率、气孔导度和净光合速率,并随着NaCl胁迫浓度的提高,下降的幅度更大,但NaCl胁迫苗木胞间隙CO2浓度明显高于对照;与对照相比,在NaCl胁迫50天后,青檀苗木的成活率、苗高和地径生长以及根系、茎和叶生物量显著降低,但茎和叶生物量下降更为明显。本文的研究结果认为,青檀是一种对盐胁迫较敏感的植物,一年生幼苗的耐盐阈值在34mM(2.0g/L)左右。图2表3参27。     

Effects of NaCl stress on seed germination, leaf gas exchange and seedling growth of Pteroceltis tatarinowii

Effects of NaCl on seed germination, leaf gas exchange and seedling growth were investigated. The germination of P. tatarinowii seeds was delayed in the presence of NaCl, and was significantly inhibited when NaCl concentration exceeded 17 mM (1.0 g·L⁻¹). NaCl treatments induced reductions of transpiration rate, stomatal conductance and net photosynthetic rate and their reductions were significant with the increasing of NaCl concentration. However, intercellular CO₂ concentration in seedling leaves under salt stress was significantly higher than that of controls. There was a significant reduction in survival, basal diameter increment and height increment with increasing NaCl concentration 50 days after NaCl treatment, and a significant reduction in the dry weight increment of roots, stems, and leaves was also observed in the NaCl treatments. The deleterious effect on the biomass increment was more evident in the case of stems and leaves. Results from this study suggest that P. tatarinowii is sensitive to salinity stress and the salinity threshold for seedling growth might be less 34 mM (2.0 g·L⁻¹). Biography: FANG Sheng-zuo (1963–), male, Professor, College of Forest Resources and Environment, Nanjing Forestry University, Nanjing 210037, P. R. China.     

Effects of the interaction between drought and shade on water relations, gas exchange and morphological traits in cork oak (Quercus suber L.) seedlings

The combined effect of drought and light on different physiological and biochemical traits was assessed in cork oak (Quercus suber L.) seedlings grown under two levels of light availability and submitted to a long-standing drought. Watering was withdrawn after germination and seedlings were allowed to dry to a water content of ca. 50% of field capacity. At this point, water-stressed seedlings were grown under moderate drought and two light regimes: high light (HL—50%) and low light (LL—2%). Soil water in control plants was kept close to field capacity (90–100%) for both light environments. Water-relations parameters derived from P–V curves, gas exchange and water status at predawn (Ψ_pd) were evaluated at twice during the experiment. Nitrogen and chlorophyll contents were determined in the same leaves used for the gas exchange measurements. In addition, maximum rate of carboxylation (V_cmax) and electronic transport (J_max) were derived from A–C_i curves in well-watered seedlings.

The variation on moisture availability during the experiment was the same under both light environments. In control plants, Ψ_pd was over −0.3 MPa at the two harvests, while stressed seedlings decreased to −0.9 MPa, with no differences between light treatments. Water stress decreased osmotic potentials at full (Ψπ₁₀₀) and zero turgor (Ψπ₀). The regressions between both potentials and Ψ_pd showed a higher intercept in shade grown seedlings. This fact will point out the higher osmoregulation capacity in sun seedlings whatever water availability.

Nitrogen investment on a per leaf mass (N_mass), chlorophyll content (Chl_mass) and SLA tended to show a typical pattern of sun-shade acclimation. Thus, the three parameters increased with shade. Only for N_mass there was a significant effect of watering, since water stress increased N_mass.

LL plants showed a lower photosynthetic capacity in terms of maximum net photosynthesis at saturating light (A_max), which was related to a decrease in V_cmax and J_max. Both parameters varied with specific leaf area (SLA) in a similar way. The low-light environment brought about a higher nitrogen investment in chlorophyll, while under high-light environment the investment was higher in carboxylation (V_cmax) and electronic transport (F_max).

Stomatal conductance to water vapour (g_wv) and A_max were lower in low-light seedlings independently of watering. In addition, there was a trend to keep higher intrinsic water use efficiency (IWUE) under high light environment. The increase of IWUE under water stress was higher in HL seedlings. This was as consequence of the steeper decline in g_wv as Ψ_pd decreased. The decrease of A_max with Ψ_pd occurred in a similar way in LL and HL seedlings. Thus, the HL seedlings tended to sustain a higher ability to increase IWUE than LL seedlings when they were submitted to the same water stress.     

Growth responses of red pine seedlings to the chemical bioregulator,DCPTA

The chemical bioregulator, 2-(3, 4-dichlorophenoxy)-triethylamine (DCPTA), which has markedly stimulated photosynthesis, carbon allocation, and above- and below-ground growth of several agricultural crops, caused small growth effects on red pine (Pinus resinosa L.) germinants and one and two-year-old seedlings, mainly to foliage and stems. At low DCPTA concentrations, i.e. 10 ppm, growth tended to be promoted, whereas at 100 ppm growth appeared to be suppressed. Continued testing of the bioregulator's effect on growth and physiology of other tree species is recommended.     

干热胁迫对杨树叶片气体交换和叶绿素荧光参数的影响

为了探讨干热胁迫对不同品种杨树叶片气体交换和叶绿素荧光参数的影响,以吴屯杨、小青杨和小美旱杨一年生嫩枝为材料,利用人工气候箱和PEG浓度控制生长温度、干旱条件,处理24 h后测定气体交换和叶绿素荧光参数以及光合色素的含量。结果表明:1)随着胁迫程度的增加,3种杨树叶片的净光合速率(Pn)和气孔导度(Gs)随着干热胁迫的程度增加均呈先上升后下降的趋势,胞间CO2浓度(Ci)则整体呈下降趋势,吴屯杨和小美旱杨的蒸腾速率(Tr)呈先上升后下降的趋势,而小青杨叶片的蒸腾速率持续增加,在重度干热胁迫时达到最大值;2)3种杨树在重度干热胁迫条件下光系统Ⅱ反应中心及其电子传递链的结构均受到了不同程度的损伤;3)3个杨树品种的类胡萝卜素含量随干热胁迫程度的增加呈稳定上升的趋势,总叶绿素与叶绿素a、b含量总体呈下降趋势。4)综合各项生理指标结果分析,3种杨树中,小青杨和吴屯杨的耐干热能力较强,小美旱杨最弱。     

Growth and photosynthetic responses of Gallesia integrifolia (Spreng.) Harms and Schinus terebinthifolius Raddi seedlings in dense shade

We analyzed the growth and photosynthetic behavior of Gallesia integrifolia (‘pau-d’alho’) and Schinus terebinthifolius (‘aroeirinha’) under shade, seeking to obtain ecophysiological information for introducing seedlings of those species in previously established cacao agroforestry systems. Considering that light intensity under the shade of cacao trees varied between 5 and 10% daylight, 5 months old seedlings were exposed to four irradiance levels (25, 17, 10 and 5% daylight) for 92 days. With shade increase both species displayed trends of decrease leaf mass per unit leaf area, leaf area per plant (LA), relative growth rate (RGR) and net assimilation rate (NAR), and increase leaf area ratio (LAR). The mean values of light-saturated net photosynthetic rate (P _nmax) in 25 and 5% daylight were 12.8 and 8.0 μmol CO₂ m⁻² s⁻¹ for G. integrifolia and 17.9 and 7.4 μmol CO₂ m⁻² s⁻¹, respectively, for S. terebinthifolius. Based on the measurements of photosynthetic photon flux density and estimated values of photosynthetic saturated irradiance (Is) we concluded that, in all shaded conditions, the leaves of both species were under sub optimal light conditions to reach P _nmax. In spite of the lowest P _nmax values, RGR and NAR were significantly higher for G. integrifolia in all irradiance levels. Differences in growth rates can be explained by the higher values of LA, LAR and leaf mass ratio (LMR), as well as by the lower values of Is, photosynthetic compensation irradiance and dark respiration rates observed for G. integrifolia. Even though seedlings of G. integrifolia presented higher capacity to adapt under conditions of dense shade, we concluded that both species were under stress conditions induced by shade in light environments below 25% daylight. On a practical point of view it is possible to conclude that seedlings of both species should be introduced in light gaps, formed after the fall of big trees, or in places in which cacao trees are cultivated using large plant spacing.     

Growth, nutrition, photosynthesis and transpiration responses of longleaf pine seedlings to light, water and nitrogen

Early growth and physiology of longleaf pine (Pinus palustris Mill.) seedlings were studied in response to light, water and nitrogen under greenhouse conditions. The experiment was conducted with 1-year-old seedlings grown in 11.3 l pots. The experimental design was a split-plot factorial with two levels (low and high) of each of the factors, replicated in three blocks. The four factorial combinations of water and nitrogen were randomly applied to 15 pots (sub-plots) in each of the light treatment (main plot). Data were collected on survival, root collar diameter (RCD), and height on a monthly basis. Biomass (shoot, root and needle), leaf area index, specific needle area, and needle nutrient (N, P, K, Ca, and Mg) concentrations were determined following final harvest after 16 months. Physiological data (net photosynthesis and transpiration) were collected monthly from March to July during the second growing season.

Height and RCD were significantly influenced by nitrogen and water and by the interaction between them with no apparent effect of light. Seedlings grew 93% taller in the high nitrogen and well watered (HNWW) treatment compared to the low nitrogen and water stressed (LNWS) treatment. Similarly, a significant increase (78%) in RCD was observed for seedlings in the HNWW treatment over the LNWS treatment. Light, along with water and nitrogen, played an important role in seedling biomass growth, especially when water was not limiting. Biomass partitioning (as measured by root:shoot ratio) was affected only by nitrogen and water. Nutrient stress had a greater influence on carbon allocation (69% increase in root:shoot ratio) than water stress (19% increase). Net photosynthesis (P_net) was significantly higher for seedlings in the high resource than in the low resource treatments with significant light×water and nitrogen×water interactions. Transpiration rate was higher (75%) under the WW treatment compared to the WS treatment. Longleaf pine seedlings grown under the LNWW treatment had the lowest foliar nitrogen (0.71%) whereas seedlings in the HNWS treatment had the highest (1.46%). Increasing the availability of light (through larger canopy openings or controlling midstory density) and soil nitrogen (through fertilization) may not result in greater P_net and improved seedling growth unless soil water is not limiting.     

Growth and photosynthetic responses of Fraxinus mandshurica seedlings to various light environments

To determine light requirement and adaptability of Fraxinus mandshurica seedlings, the seasonal variations of photosynthetic variables were measured in 3-year-old seedlings grown under four light levels (100%, 60%, 30%, and 15% of full sunlight) with a LI-6400 portable photosynthesis system. The leaf chlorophyll content, special leaf weight, annual height and basal diameter increment of seedlings were also observed. The maximum and minimum values of net photosynthetic rate, maximum rate of carboxylation, an...     

Leaf water potential and gas exchange of eucalypt clonal seedlings to leaf solar protectant

This experiment was carried out in acclimatized greenhouses with seedlings of two hybrid clones of Eucalyptus urophylla×Eucalyptus grandis. A sunscreen protector consisting of 62.5% calcium carbonate was sprayed on the seedlings at weekly intervals. Water stress was induced by suspending irrigation until the soil reached 30% available water and water was then replaced so that it returned to field capacity. Gas exchange and leaf water status were measured after 50 days. The experiment was set up in a 4×2 factorial randomized block design in four distinct environments:(1) temperatures less than 21.2℃ and vapor pressure deficit of 0.15 kPa;(2) intermediate temperatures of 24.2℃ and vapor pressure deficit of 0.69 kPa;(3) high temperatures of 27.0℃ and high vapor pressure deficit of 1.4 kPa; and,(4) high temperature of 27.0℃ and vapor pressure deficit below 1.10 kPa. Two leaf sun protector treatments were used, with five replications each. High atmospheric demand acted as a stress factor for the seedlings during the initial growth phase.Applications of leaf sunscreen protector provided beneficial effects in maintaining optimum water status and gas exchanges of the plants under water stress.     

茶条槭山梨山桃苗木对土壤水分胁迫的适应性

在温室内用盆栽法栽植了1年生茶条槭、山梨和山桃苗木,并采用4种土壤水分处理,土壤相对含水量分别为75.0%、61.1%、46.4%和35.4%。结果表明:随土壤含水量降低,3树种苗木净光合速率,蒸腾速率和气孔导度均下降,土壤含水量最低时,茶条槭苗木各生理指标降低幅度最大,山梨和山桃次之。茶条槭和山梨水分利用效率随土壤含水量的减少呈降低趋势,山桃水分利用效率呈升高趋势。水分胁迫下,3树种苗木根分配生物量显著增加。茶条槭在水分胁迫下,根冠比增加幅度最大,山梨次之,山桃最小。此外,茶条槭叶形态可塑性强,随土壤含水量降低,茶条槭单叶叶面积和总叶面积显著减小,叶厚度增加。山梨和山桃在水分胁迫下单叶叶面积及总叶面积无显著变化。综合3树种苗木在水分胁迫下的生理和形态指标及生物量分配的变化,茶条槭对水分胁迫的适应能力强于山桃和山梨。表3参31。     

Soil water stress: Its effects on phenology, physiology, and morphology of containerized Douglas-fir seedlings

Containerized Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) seedlings were subjected to six moisture-stress treatments (ranging from 7 to 65% soil water content by volume) for 12 weeks. At the end of this period, there were significant differences in phenological, physiological, and morphological responses among the seedlings in the various moisture-stress treatments. In general, seedlings grown under very high or very low soil moisture conditions were adversely affected, while those grown under moderate conditions (29 to 53% soil water content) exhibited optimum growth, bud development, and nutrient and starch reserves. The use of vector analysis was found to be helpful in data interpretation. The results indicate the importance of closely monitoring nursery moisture regimes in order to achieve the best seedling quality.     

刨花润楠对硝酸铅胁迫的生长和生理响应机制

以刨花润楠幼苗为试验材料,研究了在不同浓度硝酸铅处理下的地上和地下生长指标、保护酶活性、丙二醛、叶绿素含量以及电导率等各项生理指标.结果表明:低浓度(300 mg/L)的胁迫对刨花润楠幼苗生长有一定的促进作用,过高浓度的胁迫则抑制生长.刨花润楠幼苗叶片的总叶绿素含量以及保护酶SOD活性均随着胁迫浓度的升高呈先升后降的趋势.电导率、丙二醛含量随着胁迫浓度的升高呈现出先略降后上升的变化趋势.研究表明,刨花润楠幼苗对硝酸铅具有一定的抗性,适宜在一些硝酸铅污染地区进行推广栽植.